Wireless power receiver and power control method thereof

ABSTRACT

A method of controlling power in a wireless power receiver to wirelessly receive power from a wireless power transmitter and transmit the power to a load, the method comprising of receiving AC power from the wireless power transmitter that receives power from a power supply device, rectifying the AC power to DC power and controlling DC power applied to the load by comparing the DC power with a threshold voltage.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. patent application Ser. No.14/397,102 filed on Oct. 24, 2014, which is the National Phase of PCTInternational Application No. PCT/KR2013/003654 filed on Apr. 26, 2013,which claims the benefit of priority of Korean Patent Application No.10-2012-0044148 filed on Apr. 26, 2012, all of which are herebyexpressly incorporated by reference into the present application.

BACKGROUND OF THE INVENTION

The embodiment relates to a wireless power receiver and a power controlmethod thereof. A wireless power transmission or a wireless energytransfer refers to a technology of wirelessly transferring electricenergy to desired devices. In the 1800's, an electric motor or atransformer employing the principle of electromagnetic induction hasbeen extensively used and then a method for transmitting electricalenergy by irradiating electromagnetic waves, such as radio waves orlasers, has been suggested. Actually, electrical toothbrushes orelectrical razors, which are frequently used in daily life, are chargedbased on the principle of electromagnetic induction. The electromagneticinduction refers to a phenomenon in which voltage is induced so thatcurrent flows when a magnetic field is varied around a conductor.Although the commercialization of the electromagnetic inductiontechnology has been rapidly progressed around small-size devices, thepower transmission distance is short.

Until now, wireless energy transmission schemes include a remotetelecommunication technology based on resonance and a short wave radiofrequency in addition to the electromagnetic induction.

Recently, among wireless power transmitting technologies, an energytransmitting scheme employing electromagnetic induction or resonance hasbeen widely used.

In a wireless power transmission system employing electromagneticinduction or resonance, since an electrical signal generated between thewireless power transmitter and the wireless power receiver is wirelesslytransferred through coils, a user may easily charge electronicappliances such as a portable device.

As electric and electronic technology has been advanced and a batteryhas been used in modern times, power supply is carried out by using abattery in a wireless power transmission system.

However, in the related art, as the voltage applied to a battery ischanged, the charged state of the battery is unstable.

SUMMARY OF THE INVENTION

The embodiment provides a method of preventing a wireless powertransmission system from being erroneously operated through a powercontrol algorithm when power is wirelessly transmitted usingelectromagnetic induction or resonance.

The embodiment provides a method capable of greatly improving the powertransmission efficiency of a wireless power transmission system througha power control algorithm when power is wirelessly transmitted usingelectromagnetic induction or resonance.

The embodiment provides a method capable of stably supplying power byimproving a charged state of a battery through a power control algorithmwhen power is wirelessly transmitted using electromagnetic induction orresonance.

According to an embodiment, there is provided a wireless power receiverfor transferring power received from a wireless power transmitter to aload, which includes a reception coil to receive AC power from thewireless power transmitter; a rectifying unit to rectify the received ACpower into DC power; and a charging management unit to control DC powerapplied to the load by comparing the DC power with a threshold value.

The charging management unit may include a switch to enable therectifying unit to be connected to or separated from and the load; and acontrol unit to control the DC power applied to the load by allowing theswitch to be switched on or off according to a comparison result of theDC power with the threshold value.

The control unit may allow the load to enter the charging mode byallowing the switch to be switched on when the DC power is equal to orgreater than a first threshold value.

The control unit may allow the switch to be switched off to block asupply of the power to the load when the DC power is less than the firstthreshold value.

The control unit may allow the switch to be switched off to block asupply of the power to the load when the DC power is less than a secondthreshold value, and the first threshold value is greater than thesecond threshold value.

The control unit may transfer the DC power to the load to maintain theload in the charging mode when the DC power is equal to or greater thana second threshold value in a state that the load enters the chargingmode, and the first threshold value may be greater than the secondthreshold value.

The first threshold value may be a minimum value required for the loadto enter the charging mode, and the second threshold value may be aminimum value required for the load to maintain the charging mode.

The charging management unit may measure the rectified DC power every apreset time while the load is maintained in the charging mode.

The charging management unit may compare a voltage output from therectifying unit with a threshold voltage in order to compare the DCpower with the threshold value.

The charging management unit may further include a voltage limiting unitto absorb power exceeding a preset value when the DC power transferredto the power is equal to or greater than the preset value.

The voltage limiting unit may include a zener diode.

The reception coil may include a reception resonant coil resonantlycouple to a transmission resonant coil of the wireless power transmitterto receive the AC power; and a reception induction coil to receive theAC power from the reception resonant coil by using electromagneticinduction and to transfer the AC power to the rectifying unit.

The reception coil may receive the AC power from the wireless powertransmitter by using electromagnetic induction.

The embodiments have the following effects.

The wireless power transmission system may be prevented from being outof order and may be stably operated through a power control algorithmwhen power is wirelessly transmitted by using electromagnetic inductionor resonance.

The power transmission efficiency of the wireless power transmissionsystem may be greatly improved through the power control algorithm.

In addition, the charged state of a battery is improved through thepower control algorithm, so that it is possible to stably supply power.

Meanwhile, any other various effects will be directly and implicitlydescribed below in the description of the embodiment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing a configuration of a wireless powertransmission system according to the embodiment.

FIG. 2 is an equivalent circuit diagram of a transmission induction coilaccording to one embodiment.

FIG. 3 is an equivalent circuit of a power source and a wireless powertransmitter according to one embodiment.

FIG. 4 is an equivalent circuit of a wireless power receiver accordingto one embodiment.

FIG. 5 is a diagram showing a configuration of a resonant wireless powertransmission system according to a second embodiment.

FIG. 6 is a flowchart illustrating a power control method of a wirelesspower receiver according to a first embodiment.

FIG. 7 is a block diagram showing a wireless power receiver according toa third embodiment.

FIG. 8 is a circuit diagram showing a configuration of a control unitaccording to one embodiment.

FIG. 9 is a view showing various configuration examples of a switchaccording to one embodiment.

FIG. 10 is a flowchart illustrating a power control method of a wirelesspower receiver according to a second embodiment.

DETAILED DESCRIPTION OF THE INVENTION

In the description of the embodiments, it will be understood that, whena layer (or film), a region, a pattern, or a structure is referred to asbeing “on” or “under” another substrate, another layer (or film),another region, another pad, or another pattern, it can be “directly” or“indirectly” over the other substrate, layer (or film), region, pad, orpattern, or one or more intervening layers may also be present. Such aposition of the layer has been described with reference to the drawings.

The thickness and size of each layer shown in the drawings may beexaggerated, omitted or schematically drawn for the purpose ofconvenience or clarity. In addition, the size of elements does notutterly reflect an actual size.

Hereinafter, a light emitting device, a light emitting device package, alight unit and a method of manufacturing a light emitting deviceaccording to embodiments will be described with reference toaccompanying drawings.

FIG. 1 a circuit diagram showing a resonance-type wireless powertransmission system 1000 according to the embodiment.

Referring to FIG. 1, the wireless power transmission system 10 mayinclude a power source 100, a wireless power transmitter 200, a wirelesspower receiver 300 and a load 400.

According to one embodiment, the power source 100 may be included in thewireless power transmitter 200.

The wireless power transmitter 200 may include a transmission inductioncoil 210 and a transmission resonant coil 220.

The wireless power receiver 300 may include a reception resonant coil310, a reception induction coil 320, a rectifying unit 330 and the load400.

Both terminals of the power source 100 are connected to both terminalsof the transmission induction coil 210.

The transmission resonant coil 220 may be spaced apart from thetransmission induction coil 210 by a predetermined distance.

The reception resonant coil 310 may be spaced apart from the receptioninduction coil 320 by a predetermined distance.

Both terminals of the reception induction coil 320 are connected to bothterminals of the rectifying unit 330, and the load 400 is connected toboth terminals of the rectifying unit 330. According to one embodiment,the load 400 may be included in the wireless power receiver 300.

The power generated from the power source 100 is transmitted to thewireless power transmitter 200. The power received in the wireless powertransmitter 200 is transmitted to the wireless power receiver 300 thatmakes resonance with the wireless power transmitter 200 due to aresonance phenomenon, that is, has the resonance frequency the same asthat of the wireless power transmitter 200.

Hereinafter, the power transmission process will be described in moredetail.

The power source 100 may be an AC power source for providing AC powerhaving a predetermined frequency.

AC current flows through the transmission induction coil 210 by thepower supplied from the power source and the transmission resonant coil220 are inductively coupled with each other. When the AC current flowsthrough the transmission induction coil 210, the AC current is inducedto the transmission resonant coil 220 physically spaced apart from thetransmission induction coil 210 due to the electromagnetic induction.Thereafter, the power transferred to the transmission resonant coil 220is transmitted to the wireless power receiver 300, which makes aresonance circuit with the wireless power transmitter 200, throughresonance.

Power may be transmitted between two LC circuits, which areimpedance-matched with each other, through resonance. The powertransmitted through the resonance may be farther transmitted with higherefficiency when comparing with the power transmitted by theelectromagnetic induction.

The reception resonant coil 310 receives power from the transmissionresonant coil 220 through the resonance. The AC current flows throughthe reception resonant coil 310 due to the received power. The powertransferred to the reception resonant coil 310 is transmitted to thereception induction coil 320 due to the electromagnetic induction. Thepower transferred to the reception induction coil 320 is rectified bythe rectifying unit 330 and transferred to the load 400.

A quality factor and a coupling coefficient are important in thewireless power transmission.

The quality factor may refer to an index of energy that may be stored inthe vicinity of the wireless power transmitter or the wireless powerreceiver.

The quality factor may vary according to the operating frequency f aswell as a shape, a dimension and a material of a coil. The qualityfactor may be expressed as following equation, Q=ω*L/R. In the aboveequation, L refers to the inductance of a coil and R refers toresistance corresponding to the quantity of power loss caused in thecoil.

The quality factor may have a value of 0 to infinity.

The coupling coefficient represents the degree of inductive magneticcoupling between a transmission coil and a reception coil, and has avalue of 0 to 1.

The coupling coefficient may vary according to the relative position andthe distance between the transmission coil and the reception coil.

FIG. 2 is a circuit diagram showing an equivalent circuit of thetransmission induction coil 210 according to the embodiment.

As shown in FIG. 2, the transmission induction coil 210 may include aninductor L1 and a capacitor C1, and a circuit having a desirableinductance and a desirable capacitance can be constructed by theinductor L1 and the capacitor C1.

The transmission induction coil 210 may be constructed as an equivalentcircuit in which both terminals of the inductor L1 are connected to bothterminals of the capacitor C1. In other words, the transmissioninduction coil 210 may be constructed as an equivalent circuit in whichthe inductor L1 is connected in parallel to the capacitor C1.

The capacitor C1 may include a variable capacitor, and impedancematching may be performed by adjusting the capacitance of the capacitorC1. The equivalent circuit of the transmission resonant coil 220, thereception resonant coil 310 and the reception induction coil 320 may bethe same as the equivalent circuit shown in FIG. 2.

FIG. 3 is a circuit diagram showing an equivalent circuit of the powersource 100 and the wireless power transmitter 200 according to oneembodiment.

As shown in FIG. 3, the transmission induction coil 210 and thetransmission resonant coil 220 may be constructed by using inductors L1and L2 and capacitors C1 and C2 having predetermined inductances andcapacitances, respectively.

FIG. 4 is a circuit diagram showing an equivalent circuit of thewireless power receiver 300 according to one embodiment.

As shown in FIG. 4, the reception resonant coil 310 and the receptioninduction coil 320 may be constructed by using inductors L3 and L4, andcapacitors C3 and C4 having predetermined inductances and capacitances,respectively.

The rectifying unit 330 may include a diode D1 and a rectifyingcapacitor C5 and may convert AC power into DC power to output the DCpower.

The rectifying unit 330 may include a rectifying circuit (not shown) anda smoothing circuit (not shown).

The rectifying circuit performs a rectifying function of convertingreceived AC power into DC power.

According to one embodiment, the rectifying circuit may include at leastone diode. According to one embodiment, bridge diodes may be used as therectifying circuit.

The smoothing circuit may smooth the rectified output.

The smoothing circuit may output the stable DC current by removing aripple component from the DC power output from the rectifying circuit.

The smoothing circuit 432 may include a capacitor for smoothing.

The load 400 may be a predetermined rechargeable battery or a devicerequiring DC power. For example, the load 400 may refer to a battery.

The wireless power receiver 300 may be installed in an electronicdevice, such as a cellular phone, a laptop computer or a mouse,requiring power.

FIG. 5 is a block diagram showing a wireless power receiver 300according to a second embodiment.

Referring to FIG. 5, the wireless power receiver 300 may include thereception induction coil 320, the rectifying unit 330, the DC-DCconverter 350, and a battery management IC (BMIC) 360. According to theembodiment, if the wireless power receiver 300 receives power from thewireless power transmitter 200 through the resonance, the wireless powerreceiver 300 may further include the reception resonant coil 310.According to the embodiment, if the wireless power receiver 300 receivespower from the wireless power transmitter 200 through theelectromagnetic induction, the wireless power receiver 300 may notinclude the reception resonant coil 310.

The reception induction coil 320 receives power from the wireless powertransmitter 200. The power received in the reception induction coil 320may be AC power.

The rectifying unit 330 may convert the AC power received in thereception induction coil 320 into DC power.

The rectifying unit 330 may include a rectifying circuit 331 and asmoothing circuit 332.

The rectifying circuit 331 may include at least one diode. According tothe embodiment, the diode may refer to a silicon diode. According to oneembodiment, although the rectifying circuit 331 may perform a rectifyingfunction by using one diode, the rectifying circuit 331 may preferablyhave the structure in which at least one diode is arranged. As shown inFIG. 5, the rectifying circuit 331 may include a bridge diode as oneexample. The bridge diode structure is a circuit structure in which fourdiodes are connected to each other to perform a rectifying function.

The rectifying circuit 331 performs a rectifying function of convertingreceived AC power into DC power. According to the embodiment, since thepower is proportional to voltage or current, it is assumed that power,voltage, and current have the same concept for the convenience ofexplanation. The rectifying function refers to a function allowingcurrent to flow only in one direction. In other words, the forwardresistance of the rectifying circuit 331 is low, and the reverseresistance of the rectifying circuit 331 is sufficiently great, so thatcurrent may flow only in one direction.

The smoothing circuit 332 may output the stable DC current by removing aripple component from the DC output power of the rectifying circuit 331.

The smoothing circuit 332 may include a capacitor for smoothing.

The DC-DC converter 350 may output DC voltage suitable to operate theBMIC 360 by using the DC voltage output from the smoothing circuit 350.The DC-DC converter 350 may convert the DC voltage output from thesmoothing circuit 332 into the AC voltage, and then, may boost up ordrop down and rectify the converted AC voltage to output the DC voltagesuitable to operate the BMIC 360.

Thus, the DC-DC converter 350 may convert the input voltage into avoltage having a predetermined value and output the converted voltage.

The DC-DC converter 350 may include a switching regulator or a linearregulator.

The linear regulator is a converter to receive input voltage, provideoutput voltage by a required quantity, and dissipate the remainingvoltage as heat.

The switching regulator is a converter to adjust output voltage througha pulse width modulation (PWM) scheme.

The BMIC 360 adjusts the DC power output from the DC-DC converter 350and provides the adjusted DC power to the load 400. According to anembodiment, the load 400 may include a battery. When the load 400 is abattery, the BMIC 360 may control the DC power output from the DC-DCconverter 350 in order to stably supply power to the battery.

The BMIC 360 may be embedded in the load 400.

An amount of current charged in the load 400 may vary with the DCvoltage applied to both terminals of the load 400.

The BMIC 360 may control the DC power to provide the controlled DC powerto the load such that the load 400 is charged with a constant DCcurrent.

Operational details of the BMIC 360 will be described below.

FIG. 6 is a flowchart illustrating a power control method of a wirelesspower receiver 300 according to a first embodiment.

Details of the wireless power receiver 300 are equal to those shown inFIG. 5.

It is assumed in the following description that the load 400 is abattery embedded in an electronic appliance such as a portable phone ora laptop computer.

Referring to FIG. 6, first, in step S101, the BMIC 360 determineswhether the load 400 operates in a non-charging mode. The non-chargingmode may signify that power is not supplied to the load 400. To thecontrary, a charging mode may signify that power having a predeterminedlevel or more is continuously supplied to the load 400.

In step S103, if the BMIC 360 confirms that the load 400 is in thenon-changing mode, the BMIC 400, the BMIC 360 applies a voltage equal toor higher than a threshold voltage to the load 400. According to anembodiment, the threshold voltage may refer to the minimum voltagerequired to allow the load 400 to enter the charging mode. According toan embodiment, the threshold voltage, which is the minimum voltagerequired to allow the load 400 to enter the charging mode, may be 4.2V,but the threshold voltage of 4.2V is only one example.

Thereafter, in step S105, the BMIC 360 applies a voltage equal to orhigher than the threshold voltage to the load 400 to allow the load 400to enter the charging mode.

Then, in step S107, the BMIC 360 determines whether the voltage appliedto the load 400 is lower than the threshold voltage.

In step S109, if the voltage applied to the load 400 is lower than thethreshold voltage, the BMIC 360 blocks the voltage applied to the load400 to allow the load 400 to enter the non-charging mode. That is, whenthe voltage applied to the load 400 is lower than the threshold voltage,the BMIC 360 may determine that it is difficult for the load 400 tonormally maintain the charging mode and may block the voltage applied tothe load 400.

The voltage applied to the load 400 may become lower than the thresholdvoltage due to several reasons. For instance, it may be happen whenthere is no wireless power transmitter 200 transmitting power to thewireless power receiver 300, when the distance between the wirelesspower transmitter 200 and the wireless power receiver 300 deviates froma power transmission distance, and when the alignment directions of thewireless power transmitter 200 and the wireless power receiver 300 arenot matched with each other so that the wireless power receiver 300cannot normally receive power.

Thereafter, since the BMIC 360 does not supply power to the load 400,the BMIC 360 returns to the step S103 of applying the threshold voltageor higher to the load 400.

Then, after the step S105 is performed, if the voltage applied to theload 400 is lower than the threshold voltage in step S107, the processreturns to the step S109 of allowing the load 400 to enter thenon-charging mode.

As described above, for the external reason that the voltage applied tothe load 400 is lower than the threshold voltage, the load 400alternates between the charging mode and the non-charging mode, so thatthe load 400 may unstably operate. When the load 400 alternates betweenthe charging mode and the non-charging mode, so that the load 400unstably operates, an erroneous operation may occur in the entirewireless power transmission system.

That is, when the load 400 is a battery, due to the erroneous operationcaused by the alternate operation of the battery between the chargingmode and the non-charging mode, the durability of the battery may bereduced and the charging time for the battery may be increased.

Hereinafter, an embodiment for preventing an unstable operation of theload 400 will be described with reference to FIGS. 7 to 10.

FIG. 7 is a block diagram showing a wireless power receiver 300according to a third embodiment.

Referring to FIG. 7, the wireless power receiver 300 may include areception induction coil 320, a rectifying unit 330 and a chargingmanagement unit 370.

In addition, although not shown in FIG. 7, the wireless power receiver300 may further include a DC-DC converter 350 shown in FIG. 5.

In addition, although not shown in FIG. 7, the wireless power receiver300 may further include a battery management device (BMIC) 360 shown inFIG. 5.

The BMIC 360 may control the DC power in order to charge the load 400with a constant DC current.

The BMIC 360 may be included in the load 400. Hereinafter, it is assumedin the description that the BMIC 360 is included in the load 400.

According to the embodiment, if the wireless power receiver 300 receivespower from the wireless power transmitter 200 through the resonance, thewireless power receiver 300 may further include a reception resonantcoil 310. That is, the transmission resonant coil 220 of the wirelesspower transmitter 200 and the reception resonant coil 310 of thewireless power receiver 300 are magnetically coupled to each other andoperate at the resonance frequency. The resonance coupling between thetransmission resonant coil 220 of the wireless power transmitter 200 andthe reception resonant coil 310 of the wireless power receiver 300 mayimprove the power transmission efficiency between the wireless powertransmitter 200 and the wireless power receiver 300.

According to the embodiment, if the wireless power receiver 300 receivespower from the wireless power transmitter 200 through theelectromagnetic induction, the wireless power receiver 300 may notinclude the reception resonant coil 310.

The reception induction coil 320 transfers the AC power received fromthe wireless power transmitter 200 to the rectifying unit 330.

The rectifying unit 330 may rectify AC power to produce DC power.

The rectifying unit 330 may include a rectifying circuit 331 and asmoothing circuit 332.

The rectifying circuit 331 may include at least one diode. According tothe embodiment, the diode may refer to a silicon diode. According to oneembodiment, although the rectifying circuit 331 may perform a rectifyingfunction by using one diode, the rectifying circuit 331 may preferablyhave the structure in which at least one diode is arranged. As shown inFIG. 5, the rectifying circuit 331 may include a bridge diode as oneexample. The bridge diode structure is a circuit structure in which fourdiodes are connected to each other to perform a rectifying function.

The rectifying circuit 331 performs a rectifying function of convertingreceived AC power into DC power. According to the embodiment, since thepower is proportional to voltage or current, it is assumed that power,voltage, and current have the same concept for the convenience ofexplanation. The rectifying function refers to a function allowingcurrent to flow only in one direction. In other words, the forwardresistance of the rectifying circuit 331 is low, and the reverseresistance of the rectifying circuit 331 is sufficiently great, so thatcurrent may flow only in one direction.

The smoothing circuit 332 may output the stable DC current by removing aripple component from the DC output power of the rectifying circuit 331.

The smoothing circuit 332 may include a capacitor for smoothing.

The charging management unit 370 may measure the DC voltage applied fromthe rectifying unit 330 to a switch 371 and may determine whether toallow the load to enter the charging mode or the non-charging modeaccording to the measured DC voltage. The charging management unit 370may manage whether to charge the load 400 according to the determinationresult.

The charging management unit 370 may include the switch 371, a controlunit 373 and a voltage limiting unit 375.

The control unit 373 may control the entire operation of the chargingmanagement unit 370.

Although the control unit 373 may be included in the charging managementunit 370, the control unit 373 may be provided as a separated element tocontrol the entire operation of the wireless power receiver 300.

The control unit 373 may measure the DC voltage transferred to theswitch 371.

The control unit 373 may confirm whether the DC voltage transferred tothe load 400 is equal to or higher than a first threshold voltage andmay control the operation of the switch 371 according to theconfirmation result. According to an embodiment, the first thresholdvoltage may refer to the minimum voltage required to allow the load 400to enter the charging mode. The first threshold voltage may be the DCvoltage of 4.2V, but the threshold voltage of 4.2V is only one example.

When the DC voltage transferred to the switch 371 is equal to or higherthan the first threshold voltage, a short signal is transferred to theswitch 371 such that the switch 371 is switched on. When the switch 371is switched on, the load 400 may receive a voltage equal to or higherthan the first threshold voltage to enter the charging mode.

The charging mode may signify that constant power or greater iscontinuously supplied to the load 400.

When the load 400 is in the charging mode, the control unit 373 maymeasure the voltage applied to the switch 371 to confirm whether themeasured voltage is equal to or higher than a second threshold voltage.

According to one embodiment, the second threshold voltage may signify aminimum voltage for maintaining the charging mode of the load 400. Thesecond threshold voltage may be equal to or lower than the firstthreshold voltage. When the voltage applied to the switch 371 is equalto or higher than the second threshold voltage, the control unit 373 maymaintain the charging mode and may measure the voltage applied to theswitch 371 every a predetermined time.

When the voltage applied to the switch 371 is lower than the secondthreshold voltage, the control unit 373 may transmit an open signal toallow the switch 371 to be switch off. Thus, the load 400 deviates fromthe charging mode.

That is, the control unit 373 may confirms every a predetermined timewhether the voltage applied to the switch 371 is equal to or higher thanthe second threshold voltage to stably maintain the load 400 in thecharging mode.

When the DC power transferred to the load is equal to or greater than apreset value, the voltage limiting unit 375 may project the load 400 byabsorbing the remaining power except for the power corresponding to thepreset value. According to an embodiment, the preset value may signify amaximum voltage at which the load 400 is not damaged.

According to an embodiment, the voltage limiting unit 375 may include azener diode. The zener diode allows current to flow therethrough whenthe voltage applied to the zener diode is above a certain voltage, andis operated like an open circuit when the voltage applied to the zenerdiode is below a certain voltage so that current does not flowtherethrough.

FIG. 8 is a circuit diagram showing a configuration of the control unit373 according to one embodiment.

The control unit 373 may include a comparator configured with anamplifier and plural resistors.

The comparator may compare an input voltage V1 with a reference voltageV2 to control the switch 371. The input voltage V1 may be a voltageapplied to the load 400.

When a difference between the input voltage V1 and the reference voltageV2 is less than a specific voltage, the control unit 373 may allow theswitch 371 to be switched off. The specific voltage may be the secondthreshold voltage described with reference to FIG. 7.

When the difference between the input voltage V1 and the referencevoltage V2 is equal to or greater than the specific voltage, the controlunit 373 may allow the switch 371 to be switched on such that the DCvoltage output from the rectifying unit 330 is transferred to the load400, where the specific voltage may be the first threshold voltagedescribed with reference to FIG. 7.

FIG. 9 is a view showing various structures of the switch 371 accordingto an embodiment.

As shown in FIG. 9, the switch 371 constituting the charging managementunit 370 may include various of metal oxide semiconductor field-effecttransistors (MOSFETs).

The MOSFETs include channels including P type and N type materials, andare classified into NMOSFETs, PMOSFETs, and CMOSFETs according to thematerials.

Each MOSFET includes a gate terminal, a source terminal, and a drainterminal, and may serve as a switch by using the voltage of the gateterminal.

FIG. 10 is a flowchart illustrating a power control method of a wirelesspower receiver 300 according to a second embodiment.

An operation of the wireless power receiver 300 is essentially equal tothat described in FIG. 7. Hereinafter, since the DC power isproportional to the DC voltage, the DC power output from the rectifyingunit 330 may be replaced with the DC voltage output from the rectifyingunit 330. Likewise, the DC power applied to the switch 371 may bereplaced with the DC voltage applied to the switch 371.

In addition, in the below description, the non-charging mode may signifythat power is not supplied to the load 400, and a charging mode maysignify that power having a predetermined level or more is continuouslysupplied to the load 400.

First, in step S201, the control unit 373 transmits an open signal tothe switch 371 such that the switch 371 is switched off.

Then, in step S203, the control unit 373 stands by for 100 ms. The timeof 100 ms is only one example.

Next, in step S205, the control unit 373 measures the voltage applied tothe switch 371. The reason that the control unit 373 measures thevoltage applied to the switch 371 after the time of 100 ms is elapsed isthat the control unit 373 periodically measures the voltage applied tothe switch 371 in order to determine whether to allow the switch 371 tobe switched off.

Various schemes may be utilized as the scheme of measuring the voltageapplied to the switch 371. For example, the control unit 373 may measurethe voltage applied to the switch 371 through the comparator describedwith reference to FIG. 8.

Thereafter, in step S207, the control unit 373 confirms whether themeasured DC voltage is equal to or higher than a first thresholdvoltage. According to an embodiment, the first threshold voltage mayrefer to the minimum voltage required to allow the load 400 to enter thecharging mode. The first threshold voltage may be the DC voltage of4.2V, but the threshold voltage of 4.2V is only one example.

In step S209, if the measured DC voltage is equal to or higher than thefirst threshold voltage, the control unit 373 transmits a short signalto the switch 371. When the short signal is transmitted to the switch371, the load 400 may normally receive the DC power so that the load 400may enter the charging mode.

In step S211, the control unit 373 allows the power having a voltageequal to or higher than the first threshold voltage to be output to theload, so that the load 400 enters into the charging mode.

If the measured DC voltage is lower than the first threshold voltage inthe step S207, the control unit 373 returns to the step S201, so thatthe control unit 373 transmits an open signal to the switch 371, therebyallowing the switch 371 to be switched off.

In step S213, when the load 400 enters into the charging mode, thecontrol unit 373 measures the voltage applied to the switch 371 again.

Thereafter, the in step S215, the control unit 373 confirms whether themeasured voltage is equal to or higher than a second threshold voltage.According to an embodiment, the second threshold voltage may refer tothe minimum voltage required to allow the load 400 to be maintained inthe charging mode. The second threshold voltage is equal to or lowerthan the first threshold voltage. If it is confirmed in the step S215that the measured voltage is equal to or higher than a second thresholdvoltage, the control unit 373 stands by for 100 ms in step S217.

If the time of 100 ms is elapsed, the control unit 373 returns to thestep 213 to measure the voltage applied to the switch 371. The reasonthat the control unit 373 measures the voltage applied to the switch 371after the time of 100 ms is elapsed is that the control unit 373periodically measures the voltage applied to the switch 371 in order toconfirm whether the load 400 is maintained in the charging mode.

In step S215, if it is confirmed that the measured voltage is lower thanthe second threshold voltage, the control unit 373 returns to the stepS201 to allow the switch 371 to be switched off. That is, when thevoltage applied to the load 400 is lower than a voltage required tomaintain the charging mode, the control unit 373 allows the switch 371to be switched off so that the load 400 can be prevented fromalternating between the charging mode and the non-charging mode.

Differently from the embodiment of FIG. 6, in addition to set the firstthreshold voltage for allowing the load 400 to enter the charging mode,the second threshold voltage is further set for maintaining the chargingmode. That is, the method of controlling power of the wireless powerreceiver according to the second embodiment sets the second thresholdvoltage required to maintain the load 400 in the charging mode, so thatthe repetition of the charging mode and the discharging mode by the load400 may be reduced. For this reason, the load 400 is prevented frombeing erroneously operated, so that the operation of the wireless powertransmission system may be stably maintained.

A power control method according to the disclosure may be prepared as aprogram executable by a computer and stored in computer-readablerecording media. The computer-readable recording media include a ROM, aRAM, a CD-ROM, a magnetic table, a floppy disk, and an optical datastoring device, and include a device realized in the form of a carrierwave (for example, transmission over the Internet).

The computer-readable recording media are distributed into computersystems connected to each other through a network to storecomputer-readable codes through a distribution scheme so that thecomputer-readable codes may be executed. In addition, function programs,codes, and code segments used to realize the method can be easilydeduced by programmers in the art to which the disclosure pertains.

Although embodiments have been described with reference to a number ofillustrative embodiments thereof, it should be understood that numerousother modifications and embodiments can be devised by those skilled inthe art that will fall within the spirit and scope of the principles ofthis disclosure. More particularly, various variations and modificationsare possible in the component parts and/or arrangements of the subjectcombination arrangement within the scope of the disclosure, the drawingsand the appended claims. In addition to variations and modifications inthe component parts and/or arrangements, alternative uses will also beapparent to those skilled in the art.

What is claimed is:
 1. A method of controlling power in a wireless powerreceiver to wirelessly receive power from a wireless power transmitterand transmit the power to a load, the method comprising: receiving ACpower from the wireless power transmitter that receives power from apower supply device; rectifying the AC power to DC power; andcontrolling DC power applied to the load by comparing the DC power witha threshold voltage, wherein the controlling the DC power applied to theload includes measuring the rectified DC power and allowing the load toenter the charging mode by transferring the DC power to the load whenthe DC power is equal to or greater than a first threshold voltage,maintaining the load in the charging mode by transferring the DC powerto the load when measured DC power periodically is equal to or greaterthan a second threshold voltage in a state that the load enters thecharging mode, and blocking a supply of the DC power to the load byallowing the switch to be switched off when the measured DC powerperiodically is less than the second threshold voltage.
 2. The method ofclaim 1, wherein the controlling DC power applied to the load includescontrolling the DC power applied to the load by allowing the switch tobe switched on or off according to a comparison result of the DC powerwith the threshold voltage.
 3. The method of claim 1, wherein theallowing the load to enter the charging mode includes transferring theDC power to the load by allowing switch to be switched on.
 4. The methodof claim 1, wherein the controlling DC power applied to the load furtherincludes blocking a supply of the DC power to the load by allowing theswitch to be switched off when the DC power is less than the firstthreshold voltage.
 5. The method of claim 1, wherein the first thresholdvoltage is greater than the second threshold voltage.
 6. The method ofclaim 1, wherein blocking a supply of the DC power to the load includesblocking a supply of the DC power to the load by allowing the switch tobe switched off.
 7. The method of claim 1, wherein the first thresholdvoltage is a minimum voltage required for the load to enter the chargingmode, and the second threshold voltage is a minimum voltage required forthe load to maintain the charging mode.
 8. A method of controlling powerin a wireless power receiver to wirelessly receive power from a wirelesspower transmitter and transmit the power to a load, the methodcomprising: transmitting, by a control unit, an open signal to a switchto block a supply of a DC power to the load; measuring, by the controlunit, a first voltage applied to the switch; confirming, by the controlunit, whether the first voltage is equal to or higher than a firstthreshold voltage; transmitting, by the control unit, a short signal tothe switch when the first voltage is equal to or higher than the firstthreshold voltage; and allowing, by the control unit, the load to entera charging mode.
 9. The method of claim 8, further includes standing byfor a first time before the measuring, by the control unit, a firstvoltage applied to the switch.
 10. The method of claim 9, furtherincludes transmitting, by the control unit, a open signal to the switchwhen the first voltage is less than the first threshold voltage.
 11. Themethod of claim 8, further includes measuring a second voltage appliedto the switch when the load enters into the charging mode.
 12. Themethod of claim 11, further includes confirming, by the control unit,whether the second voltage is equal to or higher than a second thresholdvoltage; and standing by for a second time when the second voltage isequal to or higher than the second threshold voltage.
 13. The method ofclaim 12, further includes measuring a third voltage applied to theswitch when the second time is elapsed.
 14. The method of claim 12,further includes transmitting, by the control unit, an open signal tothe switch when the second voltage is less than the second thresholdvoltage.
 15. The method of claim 12, wherein the first threshold voltageis greater than the second threshold voltage.
 16. The method of claim15, wherein the first threshold voltage is a minimum voltage requiredfor the load to enter the charging mode, and the second thresholdvoltage is a minimum voltage required for the load to maintain thecharging mode.